Date: Sat, 24 Mar 90 15:00:22 EST
From: mgb@tecnet1.jcte.jcs.mil
Subject: IC-2SAT TX/RX mod

I read a posting a few weeks ago where a gentleman was interested in any
mods for the IC-2SAT that extended transmit or receive frequency range.
I didn't pay much attention to it then, but when the XYL got one for me
as a birthday present... that attitude changed markedly!  :-)

Well, I gathered up all I could find on the issue and broke out the
soldering iron and took apart the radio that was less that one day old.
                     (OH NO Mr. Bill!!!!)

Here's the straight scoop and I HAVE tried this but you still proceed at
your own risk (in case you were so foolish as to not know that :-)

Take the battery cover off the bottom and remove the two screws.
Remove two screws directly behind PTT button.
Remove one screw where handy-carry strap goes.

Gently pull on the front half of the radio and the radio will split apart
but don't pull TOO far because the front half of the radio is still attached
to the back half with that flexible plastic film wiring stuff.  Fold front
half to the right and lay it down.

WARNING:  The battery//cover release button can now pop out and a little
itsy-bitsy tiny spring can take off for parts unknown. (Ask me how I know
this... I spent 2 HOURS looking for that little sucker!)  Pull the button
out of the case NOW and watch out for that blasted little spring!

All work is done on the circuit board inside the FRONT half of the radio
(the part that you just pulled off).

EXTENDED RECEIVE:

Look along the RIGHT side of the circuit board and about halfway down the
right side you will see a tiny circuit board that is mounted VERTICALLY
on it, aligned from top to bottom.  Look at the TOP of this little tiny
board and you will see a normal diode (D-9) that is vertically mounted on
the vertical board.  Sounds confusing, but you can't miss it, it's right
on the top end of the board.

Cut this diode.  Don't try to unsolder it... CUT IT.  Take my word on it.

WARNING: Don't pull the diode away from the board and leave it hanging.
When you put the radio back together it is a very close fit and if you
short the diode, the radio won't work.  The PLL stays unlocked but no
damage will occur.  (yeah, I did that too :-)

If you stop right here and reassemble the radio, you will now have extended
RECEIVE capability after you reset the radio according to the instructions
in the manual on the first page.  And it REALLY is extended.  My PLL was
still locked up down around 88 Mhz and actually received FM broadcast
stations although it obviously sounded BAD!  :-)  The radio freq. read-out
now will go all the way up past 1 GHz, but that's just the dial read-out,
check the Channel Indicator  and when it goes to a "U" for "Unlocked" you
can keep an eye on PLL performance, however I was amazed at where the PLL
was locking up and the fact that it was actually receiving (albeit poorly)
across a very very wide range.  Yes, of course the sensitivity is way down
the further you wander from the 144-148 design frequency range but it still
is pretty impressive, and the new freqs. can be stored in memory and scanned.

EXTENDED TRANSMIT:

Look for the big IC directly in the middle of the main board on the front
cover (IC-1 40608).  Go to the bottom right corner of it. Move your eyes
slightly to the right and you will see three chip resisters in a row.
Just to the right of THOSE you will see three silk screened dots that are
bracketed by a rectangle of white ink lines where a factory diode package
would have gone.  The "dots" form a triangle with one at the top and two
at the bottom.  Install a diode (1N914 or equivalent) with the cathode
on the TOP dot and the anode on the bottom left dot.

This will give you extended transmit from about 138-163 or so.

But if you believe that trying to get a diode in there (without shorting
out a lot of stuff) is impossible, (and you are very close to being correct)
then FORGET this approach.  Instead get Icom's diode DA (# 1750000160) and
install IT in the same place.

I tried using the 1N914, and it was a TOUGH job. It worked but looked
horrible and was in imminent danger of falling off. I tried it out,
verified that it worked... and pulled it right out.  I have the diode
DA pack on order now and will do it right when it gets here. I would
politely suggest that you forget trying to use the 1N914 unless you
have a micro-miniature repair facility at hand.  (I did and still didn't
like it).

To avoid hate mail .... I have to remind you that it is illegal to transmit
on the air with this radio out of the Amateur Bands unless a legitimate
emergency exists.  (Type acceptance and all that.)

However if you (like me) plan on using it for a quick and dirty sig-gen
into a dummy load, then it is the cat's meow!

Mark Bitterlich WA3JPY
mgb@tecnet1.jcte.jcs.mil

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